Method of and means for bonding heat exchange cores



3 Sheets-Sheet 1 AIIIQ.

Alm.

Jan. 14, 1947. L E FEVER M. LEE

METHOD OF AND MEANS FOR BONDING HEAT EXCHANGE CORES Filed March 1s, 1942Jan. 14, 1947. LE FEVER M. LEE 2,414,312

METHOD 0F AND MEANS FOR BODING HEAT EXCHANGE CORES Filed March 16, 19423 Sheets-Sheet 2 INVENTOR .ZeF'everMLee ATTORNEY f Patented Jan. 14,Y1947 METHOD OF AND MEANS FOR BONDING HEAT EXCHANGE CORES Le Fever M.Lee, Buffalo, N. Y., assignor to Fedders-Quigan Corporation, Buffalo, N.Y.

Application March 1s, 1942', seriaI No. 434,874

6 Claims. 1

This invention relates to a method and means of bonding heat exchangecores of a type in which two fluids, such as air and water or air andair, respectively pass through and over a plurality of tubes to effect atemperature interchange .through the walls of the tubes. Moreparticularly, the invention is concerned with the provision of means forintegrating a tube and n or header assembly through localized fusion ofbonding material at the joints.

For illustrative purposes, it may be recalled that heat interchangers ofthis class may be made by disposing a plurality of spaced parallel tubesbetween upper and lower header plates, and putting transverse or crossns on the tubes if desired, as well as side plates and liquid receivingtanks on the headers. The metal of -which the core is made may be coatedwith solder, if the material of construction is copper or brass, or witha special alloy of aluminum and silicon if the material is aluminum, sothat, upon heating to a suitable temperature, the coating metal willmelt or fuse, run into the interstices existing at the joints, and thusbond and integrate the core elements. Such integration is desired toimpart strength and durability to the unit.

It has heretofore been proposed to effect the bonding action bysubjecting the core assembly to blasts or drafts of hot air or productsof combustion, the manufacturing operation being conducted in an oven orfurnace. It has also been proposed, in certain types of hot air furnacesnot adapted to take heat exchange cores, to reverse the direction of hotair flow periodically as a means of expediting .the heat treatment.These prior art procedures and equipment are not satisfactory, however,for the integration of cores made of very thin metal, or of materials inwhich the fusion temperature is close to the melting point of the coremetal.

Accordingly, it is among the objects of this invention to devise amethod, or operating cycle, and apparatus, in which such cores may besubjected to a fusing temperature by hot air, delivered in such Way thata close control may be exercised over the heating air, the time of heattreatment may be reduced, 4and the required power input held to aminimum. It has now been discovered that such objects may be attained bydividing the hot air flow through the core in such manner that apor-tion of the air ows in one of the available paths while theremainder of the air flows in the other of the available paths throughthe core, the two available paths, of`

course, being those utilized for heat exchange purposes when .the coreis placed in service.

When such procedure is employed, particularly if it be combined with thereverse flow effect referred to above, deviations in temperaturedifferentials throughout the core are brought to very small values, thetime cycle is greatly curtailed, and the horsepower input made afraction of that heretofore required. Apart from the savings inproduction costs so effected, the invention also permits the manufactureof such cores Without the great loss heretofore encountered from burnedor inadequately bonded assemblies, which, by reason of theirimperfections, had to be rejected and scrapped.

The appended drawings show a hot air furnace in which the describedmethod may be conducted, and for a fuller understanding of theinvention, reference may be had to such drawings, in which:

Fig, 1 is a, view, partially in side elevation and partially inlongitudinal section, through the furnace, and showing the divided airflow around the work;

Fig. 2 is a section taken on the line 2-2 of Fig. 1, or through theblower and heater end of the furnace; and

Fig. 3 is a section taken on the line 3-3 of Fig. 1, or through the workreceiving end of the furnace.

In order to simplify the description, no discussion will be attempted ofthe electric circuits for controlling the motors, or supplying currentto the electric heating elements, or regulating such circuits by controlequipment, as these may be readily understood by those skilled in theelectric furnace art. Similarly, the materials of construction are thosecommonly used, and need no specific description except to say this: whenworking with aluminum cores, fluoride fluxes may be specified. As theseare somewhat corrosive against ordinary materialsthe erection engineershould therefore specify materials of construction adapted to withstandsuch action. Otherwise, the furnace may be subjected to an unnecessarymaintenance cost.

As shown in the several figures, particularly Fig. 1, the furnacecomprises a box-like hearth portion l0 which is contiguous with adomeshaped blower and heater portion Il. Both of these portions areframed on the exterior with sheets I2 and structural shapes I3, whilethe interior of the furnace is lined with heat-resistant ceramicmaterial I4. 'Ihis lining may, if desired in 'connection with minimizingcorrosion, be

faced oil with corrosion-resistant steel I5. The furnace, as thus fardescribed, is formed internally with ducts and passageways through whichthe hot air may be circulated over and through the work.

The left hand end or blower portion of the furnace is formed with aninternal pedestal I6 receiving a bearing |1, and with an externalsupport I8 mounted on one of the columns |3 which receives anotherbearing I9. These bearings are aligned to receive a blower shaft 2|,driven by a motor 22 through suitable belts 23. A squirrel Icage typeblower 24 is mounted on the shaft 2| within the portion I I to circulatethe air.

In Figs. 1 and 2, the discharge side of the blower 24 is shown asdelivering into a feed duct 26, while air is returned to the intake sideof the blower through a duct 21, which is offset in order to supplyreturned air to both sides of the blower. To this end, the peripheral ordisch-arge side of the blower 24 is shrouded by forming the liner Iadjacent the inlet side 26 (which portion of the liner is heredesignated by the numeral 28) as a scroll which closely approaches theblower on its under side and diverges therefrom into the main portion ofthe duct 26. The duct 21 merges into a back duct 29 provided in the rearof the wall 28, which in turn terminates in a side chamber 3| disposedoppositely to the upper end of the duct 21. Air entering through theduct 21 therefore is divided by the back duct 29 and chamber 3| into twoportions, and thus may enter the blower 24 from either side. As lthe airis driven by the blades of the blower, it emerges through the peripheryinto the chamber formed therebetween and the scroll 28, and so isdirected into the feed duct 26.

The duct 26, adjacent the blower 24, is provided with a plurality ofheating elements 33 which may conveniently be mounted on a panel section34 which abuts the outer wall I 2 of the furnace, and which protrudeinto the duct 26 through a side opening 35. During operation, the panel34 is covered with a removable wall section 36 to avoid unnecessary heatlosses and protect the heating elements from damage. The elements 33 maybe of any desired type, either electric resistors or gas-fired quartztubes, but for present purposes the resistor type is preferred. Currentis supplied thereto in the usual way, and temperature-responsiveregulators should be included in the circuits so as to maintain the airat the desired temperature.

The blower and heater portion through the duct 26, merges into thehearth or work-receiving portion IU at the lower end of the duct 26, andthe arrangement of-the portion I6 is such that the hot air is dividedfor dual flow through -t'he work, and also reverse flow, beforereturning through the duct 21 to the blower 24 for recirculation andreheating. Some of the constituents of the portion Ill are: a perforatework supporting platform or hearth 4|, upper and lower air passages 42and 43 disposed in series through the platform 4 and means, such as adamper 44, for directing the hot air from the duct 26 through thepassages and the platform and thence into the return duct 21.

It will be seen that the upper passage 42 is partially separated fromthe duct 26 by a depending wall 45, and is spaced from the return duct21 by a bridge 46 formed with an overhanging portion 41 and a wall 48.The lower passage 43 is also separated from the return duct 21 by abridge 49. Each passage, however, may be placed in communication withthe ducts 26 or 21 through ter- ,4 minal portions 42a, 43a,respectively, in which are located curved baille plates 5|, 52. Similarbaffles 53 are disposed at the lower end of the duct 26 to direct thehot air uniformly into the passageways as conditions permit.

The platform 4| is formed as a grid of intersecting bars, and extendsfrom the edge of the bridge 49 to the back wall 54 of the passage 43,baflles 55 in the passage serving to direct and distribute the air overthe platform. The left hand portion of the platform, as it will benoted, underlies the overhanging section 41 of the upper bridge 46. Theupper passage 42 is offset to the right, as indicated by the referencenumeral 56, and it also contains flow-directing ballles or plates 51.

The side walls of the portion I0, as best shown in Fig. 3, are providedwith aligned openings 6| adjacent the platform 4|, and with slidingcover doors 62 guided between angle irons 63. The doors may be suspendedby cables 64 passing over pulleys 65 mounted on an axle 66, which inturn is supported on posts 61 on top of the portion |Il. Roller tracks68 are positioned at either side of the furnace, at the level of theplatform 4I, so that the assembled cores C may be pushed in on one side,and withdrawn from the other.

It will be seen, particularly from Fig. l, that the core is so locatedin the furnace, on the platform 4|, as to abut the overhanging end 41 ofthe bridge 46, and be spaced from the back region 56 of the passage 42.This accordingly and automatically provides a split or dividedpassageway from passage 42 to passage 43-namely, in a vertical directionthrough the core C, and in a longitudnal direction. When cores 0fvarying sizes are to be treated, shut-off plates or adapters may be laidagainst and on the portion 41 or platform 4| as desired, so as tomaintain this dual path. The construction just described is preferred toadditional duct work for dividing the air current, because of itssimplicity and adaptability to most conditions.

The above noted damper 44, employed to effect reversal orshort-circuiting of the air path between the inlet 26 and the returnduct 21, `:onsists of a flat plate 1I mounted on a shaft 12 which isborne by an internal bushing 13 (Fig. 2) and a sleeve 14. Circularguards 15 are also positioned on the shaft adjacent the supportedportions to reduce leakage along the sleeve and to protect the bearingsfrom undue effects of the air current. The shaft 12 and the plate 1| areoperated in unison by a small motor 16 driving a speed reduction gearingunit 11 to which the shaft is connected. This motor, depending upon theintended plan of operation, may be energized through automaticallyactuated controls to turn the damper 44 to one operative position, andthen to the other by rotation, and again to a neutral position, in timedsequence. Or, in someinstances, such control may be dispensed with, andthe positioning of the damper may be done manually.

'In either event, it will be clear from Fig. 1 that the damper 44 may bedisposed in any desired angular position. Thus, it may extend from thelower left corner of the bridge 46 to the diagonally opposite corner ofthe duct 26. ln such case, flow will occur in the following circuit:From ductl 26 into passage 42 via throat 42a, thence over deflectors 51down through the core C, and simultaneously from end region 56longitudinally of the core to the region under overhanging bridgeportion 41. through adjacent portions of the open-work of Both flowspass 90, then the plate 1I will extend from the lower edge of wall 45 tothe diagonally opposite corner of lower bridge 49, and the air flow fromthe duct 26 to the return 21 will be just the reverse of that traced.The deflectors 55 will serve to divide the air stream, part of the airpassing upwardly through the core, and the remainder passing through theapertures in the platform 4| for longitudinal flow. When the damper isplaced midway between its terminal points, a short-circuit ing path isprovided between ducts 26 and 21 as a path of least resistance, and willthus minimize heavy losses of heated air when the doors 62 are opened toinsert or remove a core.

Alternatively, or in connection with the shortcircuiting of the ducts,the heat supplied to the elements 33 may be interrupted when the doorsare opened, and the blower 24 may also be shut down. With heat exchangecores of the type hereinafter more specifically considered, one door 62may be partially opened at the end of the heating period, and the workpermitted to remain on the platform 4I. If the heat input to -theelements 33 is then interrupted, and the blower 24 continued inoperation, a cooling draft of fresh air will enter the circuit, thusreducing the temperature of the work to a point where it may be handledwith greater safety and convenience.

It has heretofore been noted that hot air furnaces, anddevices foreffecting a reversal of air flow, have heretofore been made, but none ofthem has been adapted to the development of the divided iiow justdescribed. In order to point out more clearly the significance of thenew furnace, the steps or method of bonding a heat exchange core will bedescribed.

For exemplary purposes, reference may be made to a tube and fin coreassembly in which thin aluminum is used as the material of construction,the heat exchanger is formed with several hundred tubes, and it isdesired to bond with aluminum-silicon alloy in order to integrate thestructure. Since the alloy fuses at a temperature of say l1701180 Fahr.,and the metal itself will melt at about 12201230, it is apparent that amaximum temperature dilerential of only about 50 Fahr. is available,thus making the control of temperature an extremely diflicult problem,even with modern precision instruments and regulators. It is, however,possible to hold the temperature of the air emerging from the duct 26toa fairly close and satisfactory value.

The problem therefore arises in limiting the temperature gradientsthrough the core C itself, bringing al1 parts to temperature in aminimum of time, and avoiding such air velocities through the Work aswill tend to distort, and therefore injure, its relatively fragilestructure at the high temperatures.

It will be apparent that the hot air blown over the work will lose someof its heat thereto, and thus, under ordinary conditions, and to bringthe entire core up to bonding temperature at its most inaccessiblepoints, it is necessary to overheat the core at the points of initialcontact. Thus, in s employing a single blast or air current, thepossibility of burning cannot be eliminated. Similarly, it is nowapparent that the customary reversal of air current, while serving toexpose opposite surfaces to initial contact, still does not suffice toreach the remote parts of the work in a satisfactory manner. By dividingthe air stream for dual flow in intersecting directions through thecore, and by superimposing the reversing effect, however, the maximumthermal paths from initial contact points to remote points is reduced toa minimum. This avoids the burning condition heretofore encountered, andalso curtails the time required to bring the core up to temperature.

Another factor pertaining to the split or dual circulation relates tothe power consumed in supplying the air to the hearth. In one type offurnace, as a comparative example, it was found that a fifty horsepowermotor was required to operate a blower delivering 10,000 c. f. m. of hotair passing through thework in one direction. According to the presentinvention, however, wherein the air is divided into two streams, it issufficient, for the same size core, to supply '1,000 c. f. ml at thesame temperature, using the input of a ten horsepower motor. Theexplanation of this surprising reduction in power consumption is in thecircumstance that since the heating air has a much greater area throughwhich to pass, it may pass through the core with less resistance orpressure drop. Since the power input rises as the cube of theresistance, the dual paths permit the accomplishment of the desiredresult with less air and less power.

In applying this method to heat interchangers as described, the work Cis inserted into the furnace onto the platform 4I, the damper 44 beingthen at a neutral or short-circuiting position. The doors 62 are closed,and the damper is turned to one of its diagonal positions to direct theair flow through one or the other of the effective paths. Since the coreC may be readily located on the platform, the dual paths areautomatically determined, as heretofore described. Reversal of ow can beeffected by the settings of the motor 16, and it may be any value foundsuitable by experience. Thus, if the core can be brought to temperaturein six minutes, the damper 44 may be reversed every half minute, and fora nine minute heating cycle, reversals may be made every minute. As soonas the whole work has been brought to the bonding temperature, thedamper should be returned to neutral, and the work removed, sinceprolonged heating may be actually detrimental and could serve nobeneficial purpose.

For other types of work, it will be apparent that the cycles will bemodified to suit the occasion, and it will also be apparent that undersome conditions the reversal of flow may be omitted, since the savingsincident to the provision of dual pathways may be obtained withoutresort to this step. The great advantage of reversing is, of course, toshorten the time cycle.

It will also be apparent to those skilled in the art that while theinvention has been described with reference to one specific form ofapparatus and the processing of a designated type of core, theprinciples may be otherwise embodied, and therefore it is intended thatthe foregoing description be considered as illustrative, and that thescope of the inventionY should not be restricted thereto, but should bedeemed commensurate with the following claims.

I claim:

1. A hot gas furnace having a blower portion including a blower andheating means for circulating and heating air, inlet and return ductsrespectively delivering the air from and inducting it to the blower, anda, hearth portion connec'ted to the blower portion through said ducts,said hearth portion including a pair of spaced passages, a perforateplatform positioned between the passages, one of said passages having anolset portion and an overhanging portion member disposed in one of saidpassages and overhanging a portion of the platform thereby to provide,with respect to work positioned on the platform, dual paths between saidpassages, inlet and return ducts respectively connected to the passages,a blower portion communicating with the opposite ends of the ducts, andmeans in the blower portion for heating and recirculating the hot gas tosaid passages.

3. A hot gas blast heating furnace comprising a hearth portion and aiblower portion and ducts extending between and through said portions toform a cyclic ow path, said hearth portion having a pair of spacedpassages forming parts of the path, a work-receiving platform positionedin the hearth portion and dividing the passages from each other, aninlet duct and a return duct spaced from said platform, each of saidducts being in open communication with said spaced passages, a dampermovable to connect the inlet duct with one or the other of the passagesand the return duct with the other or one of said passages, said inletand return ducts extending to said blower portion, a blower mounted inthe blower portion, said blower having a suction side and a dischargeside, said return duct terminating in the blower portion at the suctionside thereof, saidinlet duct connecting with the discharge side of theblower, and air heating means disposed in the inlet duct between thedist charge side of the blower and said damper.

4. A hot gas blast furnace comprising an elongated portion having aninternal end wall provided with a horizontal section, a pair of bridgesdisposed transversely of the portion remote from the said end wall,- aperforate platform extending from said horizontal section to one of saidbridges, flow passages formed in the portion above and below theplatform and bridges, one of the bridges overhanging a portion of theplatform, a work entry opening in the portion to permit the placement ofwork on the platform between the horizontal section and the overhangingbridge, a b lower and heater portion disposed contiguously to theelongated portion, ducts extending between said portions, and means forconnecting the ducts and passages in a closed circuit extending throughthe platform.

5. Ahot gas furnace comprising a box-like structure having a blowerportion and a hearth portion, means in the hearth portion to supportwork to be heated by the hot gas and passages adjacent said supportingmeans to receive hot gas from and return it to said blower portion, saidblower portion including a dome, a rotary blower mounted in the dome, ascroll surrounding the periphery of the blower and terminating in aninlet duct, said inlet duct extending from said dome to the hearthportion and communicating with at least one of the passages therein,heating elements mounted in the duct to supply heat to the gas deliveredby the blower, a back duct behind the scroll-and merging into sidechambers at either side ofthe blower, and a return duct communicatingwith the black duct and side chambers and extending to the hearthportion and communicating with at least one of the passages therein.

6. A hot gas furnace comprising a blower and heater portion and a hearthportion, said blower portion being located at the end and partially toone side of the hearth portion, upper and lower passages formed in thehearth portion, said passages being divided by a Work-receiving platformand being separated by upper and lower bridges, a return 'duct extendingfrom between the bridges to the blower portion, an inlet duct extendingfrom the blower portion to the hearth portion, said inlet duct andpassages being located in quadrantal positions to each other, a rotarydamper mounted between the duct and passages adjacent the bridges, andmeans for rotating the damper to different angular positions to connectthe inlet duct and the return duct successively to first one passage andthen the other.

LE FEVER M. LEE.

